Effects of the Parkinsons Disease associated protein LRRK2 on lysosomal function and inflammatory activity in microglia

Northwestern University At Chicago, Evanston IL

Investigators

Abstract

Project Summary: Examination of genetic risk factors for Parkinson’s disease (PD) has allowed for the identification of key mechanisms contributing to the pathogenesis of this disorder. Mutations in the gene encoding leucine-rich repeat kinase 2 (LRRK2) are the most common cause of familial PD and pathogenic LRRK2 mutations are also found in approximately 1% of idiopathic PD cases. Multiple lines of evidence point towards LRRK2 as playing an important role in immune system regulation, including the finding that LRRK2 is highly expressed in both peripheral macrophages as well as microglia, the resident immune cells of the central nervous system (CNS). Furthermore, evaluation of PD-specific risk variants in LRRK2 has demonstrated that these variants are associated with microglia-specific changes in LRRK2 expression. The pathogenic LRRK2 G2019S mutation has been shown to lead to lysosomal dysfunction in dopaminergic neurons through multiple mechanisms, including modulation of the lysosomal enzyme glucocererbrosidase (GCase) which is encoded by GBA1, another PD risk gene. Induced pluripotent stem cells (iPSCs) derived from PD patients with known genetic mutations provide an ideal platform to define specific mechanisms by which PD-associated genes contribute to microglial dysfunction. Our preliminary data shows that iPSC-derived microglia with the LRRK2 G2019S mutation exhibit reduced lysosomal uptake of multiple substrates as well as impaired lysosomal protease activity. I hypothesize that the LRRK2 G2019S mutation leads to lysosomal dysfunction in microglia at least in part through modulation of lysosomal GCase and that lysosomal stress in microglia alters downstream inflammatory signaling. I additionally hypothesize that inflammatory factors produced by LRRK2 mutant microglia contribute to lysosomal dysfunction and oxidative stress in dopaminergic neurons. In Aim 1, I will investigate how LRRK2 and GBA1 interact to regulate lysosomal function and phagocytosis of alpha-synuclein and myelin in iPSC-derived human microglia. I will then evaluate the impact of mutations in these genes on cytokine secretion profiles and transcriptional states of iPSC-derived microglia in response to exposure to CNS substrates. In Aim 2 I will co-culture iPSC-derived microglia and dopaminergic neurons to assess whether factors produced by LRRK2 mutant microglia contribute to lysosomal dysfunction and oxidative stress in dopaminergic neurons and define specific mediators of dopaminergic neuron vulnerability. The overarching goal of this project is to identify signaling pathways downstream of LRRK2 that could serve as potential targets for the development of therapies designed to slow PD progression. The proposed research strategy and career development plan will provide me with critical tools to launch my career as an independent physician scientist, including developing expertise in iPSC technologies, transcriptomics, and neuroimmunology. This award will ultimately provide me a platform to cultivate a research program studying the complex interplay between genetics and neuroinflammation in PD and other degenerative movement disorders.